This invention pertains generally to gauging devices for fluids and more particularly to a device for determining the location of the interface between stratified liquids of different character such, for example, as oil and water.
In gauging tanks holding liquids such as petroleum by ullage readings it is difficult to determine with any certainty the quantity of that liquid if water is also present or likely to be present in a stratified area beneath the liquid. Such may occur if the liquid has been subject to contamination by water or, most importantly, where a vessel has been involved in a casualty involving penetration of a petroleum cargo or fuel tank with attendant ingress of water into that tank. In such cases it is very important to quickly determine the quantities of petroleum remaining to ascertain both the amount lost for pollution control planning and the amount remaining for emergency off loading requirements.
Since, due to their relative densities, petroleum and water will stratify with water layered beneath the petroleum, some means must be provided to remotely sense the quality of water underlying the petroleum. This has been accomplished in the past by means of electronic sensors which detect the differing character of petroleum and water by sensing their differing electrical conductance characteristics. By lowering the device through the petroleum into the water, the interface between the two liquids can be determined by noting the point of deployment of the sensor at which the electrical conductance changes. Such devices work well so long as the petroleum is relatively light and of low viscosity. When the petroleum, however, is heavy and viscous such as would be the case with a cold or cooling #6 residual fuel oil, the above sensor would not be suitable since it would be coated by the viscous oil as it is passed through it and be therefore incapable of sensing the changed character of the water once it passes through the interface. In attempts to avoid this problem, where a tank vessel with a holed fuel tank was awaiting drydocking, a probe was lowered to the bottom of the holed tank through viscous oil while immersed in a container of water and subsequently raised out of the container and through the interface in an attempt to detect the change in conductivity on the way back through. Although extreme care was exercised and the attempt repeated several times, no success was experienced in so locating the interface.